Dendritic Integration and Direction Selectivity in Starburst Amacrine Cells

描述(申请人提供)：在视网膜中，方向选择性神经节细胞对顺向移动的光刺激产生许多动作电位，而对相反方向的光刺激产生很少的动作电位。星爆型无长突细胞树突状细胞不对称释放γ-氨基丁酸(GABA)被认为是使这一方向选择性调谐到方向选择性神经节细胞的原因。星状突起的无长突细胞在受到从胞体向胞体远侧树突移动的光的刺激时，在靠近GABA释放部位的远端树突内表现出比从远侧树突朝向胞体的光更多的钙离子增加。这种钙离子水平不对称的来源和后果还不是很清楚。在这个提议中，我探索了恒星爆裂无长突变体的假设 在单个树突中，细胞自主地计算方向。树突如何整合其输入具有广泛的重要性，因为它是所有具有多个输入的神经元中神经元信号传递的关键步骤之一。星爆无长突细胞与许多其他类型的细胞不同，因为它们的结合点位于树突的远端，而不是胞体。此外，与许多其他类型的神经元相比，星爆无长突细胞如何整合其输入的问题与细胞的已知生理功能有关。输入的顺序与移动光刺激的方向直接相关。因此，了解星暴细胞树突中的整合将直接有助于我们理解 星状突起的无长突细胞在视网膜回路中的作用。利用电生理学，谷氨酸 我将利用分离和成像技术，确定星爆细胞树突的内在非线性是否有利于从胞体向远端树突释放部位顺序到达的双极细胞输入，而不是以相反顺序到达的输入(目标1)。此外，我建议进行实验，以确定先前观察到的刺激远端树突状细胞时钙离子的增加是否会导致星状突起的无长突细胞对方向选择性神经节细胞的抑制增加(目标2)。最后，我建议通过实验来确定电压门控钙通道在星状突起无长突细胞树突状细胞钙离子内流和GABA释放的不对称性中的作用(目标3)。

DESCRIPTION (provided by applicant): In the retina, direction selective ganglion cells fire many action potentials in response to light stimuli moving in a preferred direction and few action potentials to light moving in the opposite direction. Asymmetric release of gamma-aminobutyric acid (GABA) from starburst amacrine cells dendrites is thought to confer this direction selective tuning to direction selective ganglion cells. Starburst amacrine cells have been shown to exhibit a larger increase in Ca2+ in their distal dendrites near GABA release sites during stimulation with light moving from their soma toward the distal dendrites compared with light moving from the distal dendrites toward the soma. The source and consequence of this asymmetry in Ca2+ levels are not well understood. In this proposal, I explore the hypothesis that starburst amacrine cells compute direction autonomously in individual dendrites. How a dendrite integrates its inputs is of broad importance because it is one of the key steps in neuronal signaling in all neurons with multiple inputs. Starburst amacrine cells are distinct from many other cell types because their integration point is located in the distal end of the dendrite rather than at the soma. In addition, in contrast to many other neuron types, the question of how the starburst amacrine cell integrates its inputs is relevant to the known physiological function of the cell sine the order of inputs is directly related to the direction of moving light stimuli. Therefore understanding integration in starburst cell dendrites will contribute directly to our understanding of the role of starburst amacrine cells in the retinal circuit. Using electrophysiology, glutamate uncaging and imaging techniques, I will determine whether an intrinsic non-linearity in the starburst cell dendrites favors bipolar cell inputs arriving sequentially from the soma toward the release sites in the distal dendrites over inputs arriving in the opposite order (Aim 1). In additin, I propose experiments to determine whether the previously observed increase in Ca2+ during stimulation toward distal dendrites leads to an increase in inhibition from starburst amacrine cells onto direction selective ganglion cells (Aim 2). Lastly, I propose experiments to determine the role of voltage-gated Ca2+ channels in establishing the asymmetry in Ca2+ influx and GABA release from starburst amacrine cell dendrites (Aim 3).